巨型病毒拥有最大的构建蛋白质的基因集

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本周《自然 - 通讯》发表的一项研究报告发现了巨型病毒 Tupanvirus 的两个毒株。该病毒包含所有已知病毒中蛋白质组装所需的最全的基因集，通过它们可以了解病毒的演化。

巨型病毒的发现引发了有关病毒演化的激烈争论，主要理论有两种。一种认为复杂的巨型病毒由简单的祖先通过获取被感染宿主的基因演化而来。另一种认为巨型病毒的祖先可能已经是巨型病毒，不需要的基因随着时间的推移而丧失。

Bernard La Scola 及同事在从巴西一个碱湖和深海沉积物收集的样本中发现了 Tupanvirus。对这些病毒的基因组进行分析后发现，它们包含了与已知病毒以及三种生命域（古菌域、细菌域和真核域）的生物体类似的基因。但是，其中约 30% 的基因的同源基因尚未在其它生物体中发现。

作者对比其它病毒后发现，Tupanvirus 包含了参与蛋白质组装的最大的基因集，而且拥有将所有 20 种氨基酸组装成蛋白质所需要的基因。这 20 种基因的起源目前仍未可知。 作者总结表示，虽然有必要展开进一步的研究，但是 Tupanvirus 的发现意味着人们向理解病毒演化迈进了重要一步。

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Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphere

Jônatas Abrahão, Lorena Silva, Ludmila Santos Silva, Jacques Yaacoub Bou Khalil, Rodrigo Rodrigues, Thalita Arantes, Felipe Assis, Paulo Boratto, Miguel Andrade, Erna Geessien Kroon, Bergmann Ribeiro, Ivan Bergier, Herve Seligmann, Eric Ghigo, Philippe Colson, Anthony Levasseur, Guido Kroemer, Didier Raoult & Bernard La Scola

Here we report the discovery of two Tupanvirus strains, the longest tailed Mimiviridae members isolated in amoebae. Their genomes are 1.44–1.51 Mb linear double-strand DNA coding for 1276–1425 predicted proteins. Tupanviruses share the same ancestors with mimivirus lineages and these giant viruses present the largest translational apparatus within the known virosphere, with up to 70 tRNA, 20 aaRS, 11 factors for all translation steps, and factors related to tRNA/mRNA maturation and ribosome protein modification. Moreover, two sequences with significant similarity to intronic regions of 18 S rRNA genes are encoded by the tupanviruses and highly expressed. In this translation-associated gene set, only the ribosome is lacking. At high multiplicity of infections, tupanvirus is also cytotoxic and causes a severe shutdown of ribosomal RNA and a progressive degradation of the nucleus in host and non-host cells. The analysis of tupanviruses constitutes a new step toward understanding the evolution of giant viruses.

https://www.nature.com/articles/s41467-018-03168-1